Japanese and South Korean researchers plan to observe the asteroid Ryugu, on which the Hayabusa2 unmanned spacecraft successfully landed twice, through a telescope on the ground this autumn. The team of researchers are hoping to learn more about the asteroid, such as its origin, by investigating the existence of fine particles the Hayabusa2 probe may not have been able to detect.
In late December, Ryugu will be the closest to Earth it has been since the asteroid was discovered in 1999. The distance from our planet will be reduced to about 9 million kilometers, which is about 25 times the distance between Earth and the moon.
Taking advantage of the opportunity of being able to observe the asteroid at its brightest from Earth, the researchers plan to observe the asteroid between October and December with the 1.6-m Pirka Telescope installed at Nayoro Observatory of Hokkaido University in Noyoro, Hokkaido, among other instruments.
Hayabusa2 have found out so far that the surface of Ryugu is rocky, with fine particles rising from the surface when the probe touched down on the asteroid. However, the camera installed on Hayabusa2 is only capable of capturing particles larger than 1 millimeter. Therefore, researchers are going to investigate from the ground whether there are particles smaller than that.
The team said determining whether fine particles exist on Ryugu will help them learn about the changing process of the asteroid, such as the effect of heat to which the asteroid has been exposed in the past.
To observe fine particles, the researchers will utilize the polarization of light coming from the asteroid. When sunlight hits the surface of the asteroid and reflects, polarization -- in which light vibrates in a specific direction -- will be observed. The vibration will help researchers extrapolate the possible existence of particles measuring 0.1 millimeters to 0.001 millimeters.
In November or December, Hayabusa2 will return to Earth with samples believed to have been collected when it had landed on Ryugu.
"We're hoping to learn more about Ryugu through examining the samples brought [by the probe] together with observations of the asteroid from the ground, and other factors," said Prof. Masateru Ishiguro of Seoul National University, who specializes in solar system.
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